This Error event indicates that Microsoft Office Outlook Web App did not proxy or redirect requests from a computer that is running the Client Access server role to a Client Access server that is located in a different Active Directory site. A symptom of this failure is that the user referenced in the event description could not log on to their mailbox using Outlook Web App through the Client Access server in a different site. This event may occur when the service discovery process returns a malformed URL address of the remote Client Access server.

To resolve this error, make sure that the msExchInternalHostName (Internal URL) and msExchExternalHostName (External URL) attributes of the Outlook Web App virtual directory of the remote Client Access server are formatted correctly.

You correct these values by using a tool such as Active Directory Service Interfaces (ADSI) Edit, the LDP (ldp.exe) tool, or any other Lightweight Directory Access Protocol (LDAP) version 3 client.

Your URLs should be in the following formats:

• If Secure Sockets Layer (SSL) is used to proxy the request, use the format: msExchInternalHostName: https://InternalFulllyQualifiedDomainName/owa
  
  
• If HTTP is used to proxy the request, use the format: msExchInternalHostName: http://InternalFulllyQualifiedDomainName/owa
  
  
• If SSL is used to redirect the request, use the format: msExchExternalHostName: https://ExternalFulllyQualifiedDomainName/owa
  
  
• If HTTP is used to redirect the request, use the format: msExchExternalHostName: http://ExternalFulllyQualifiedDomainName/owa
  
  Note   By default, msExchExternalHostName is blank. This external URL attribute is only needed if the Client Access server is Internet-Facing. If the Client Access server is Internet-Facing, this URL is only needed to enable the incoming Outlook Web App request from another Client Access server to be redirected to the specified external URL address.
  
  Caution   If you incorrectly modify the attributes of Active Directory objects when you use ADSI Edit, the LDP tool, or another LDAP version 3 client, you may cause serious problems. These problems may require that you reinstall Windows Server, Microsoft Exchange, or both. Modify Active Directory object attributes at your own risk.
  
  

To correct an internal or external URL:

1. Open an Active Directory editor such as ADSI Edit.
   
   
2. Expand Configuration <DomainName>, expand CN=Services, and then expand CN=Microsoft Exchange.
   
   
3. Expand CN=<ExchangeOrganizationName>, expand CN=Administrative Groups, and then expand CN=<AdministrativeGroupName>.
   
   
4. Expand CN=Servers, expand CN=<ServerName>, expand CN=Protocols, and then expand CN=HTTP.
   
   
5. Under CN=HTTP, right-click CN=owa (Default Web Site), and then click Properties.
   
   
6. In the Attribute Editor, click the msExchExternalHostName or msExchExternalHostName, and then click Edit.
   
   
7. In the Edit Attribute box, set the value to the appropriate format.
   
   
8. Click Apply, and then click OK.
   
   
9. Close ADSI Edit.
   
   

• Contact a Microsoft Support professional to resolve this issue. To contact a Microsoft Support professional, visit the Exchange Server Solutions Center. In the navigation pane, click Assisted Support Options and use one of the assisted support options to contact a Microsoft Support professional. Because your organization may have a specific procedure for directly contacting Microsoft Technical Support, be sure to review your organization's guidelines first.
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.